"Modern humans adopted innate immune genes responsible for recognizing invading microbes from Neanderthals and Denisovans, according to two studies published today (January 7) in The American Journal of Human Genetics. The two teams, based in France and Germany, independently concluded that humans picked up some versions of a cluster of toll-like receptors by interbreeding with archaic hominin relatives.

'Once humans came out of Africa and then encountered archaic species, they might also have encountered their pathogens, said Rasmus Nielsen, an evolutionary biologist at the University of California, Berkeley, who was not involved in the studies. There might have been pathogens that could affect Neanderthals and Denisovans that also could jump into modern humans.

'At least partially, Neanderthals may have harbored already adaptive mutations, mutations that rendered them more resistant to infections, said Lluis Quintana-Murci, an evolutionary geneticist at the Pasteur Institute in Paris and a coauthor of one of the new papers.

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"And the reduced H. pylori prevalence associated with the borrowed TLR alleles is simply a sign that the variants are associated with altered immunity, not necessarily an indication that breeding with Neanderthals helped humans avoid this particular pathogen. We may not have the pathogens around today that selection was acting in response to, said Nielsen.

"The studies help confirm that interbreeding between humans, Neanderthals, and Denisovans shaped human evolution, sometimes offering key advantages people of combined lineage. The things that modern humans took away from the interbreeding with the Neanderthals were regions of the genome involved in adaptation to the environment, said Kelso."